The present invention relates to the field of controllers for printers and, more particularly, to the use of an auxiliary control device within a color thermal printer for managing printing and/or paper handling functions.
Printers continue to become more and more sophisticated, in response to commerce demanding increasingly more functionality from printers. Adding to the complications created by this situation, printing speeds have also become higher. Even though microprocessors suitable for performing control functions within printers have increased in sophistication, the demands upon the microprocessors have outpaced their development. The need for optimum communication between a printer and its host has placed additional demands upon the printer""s built-in processor.
Thermal printers introduce yet another level of complication: the characteristics of the thermal print head change from character to character. This means that a character printed with a cold print head may appear on the media differently than do characters printed after the head is warm. In some applications, the quality of the print is critical. In other applications, good print quality, while not critical, may cause a customer to select one printer over another because of subjective differences in print quality. The added complexity of color (i.e., two or more color) thermal printers demands even more control of printing parameters.
Sophistication is required to manage the thermal hysteresis in the print heads. One such management tool known to those skilled in the thermal printer arts is called xe2x80x9cdot historyxe2x80x9d. In a dot history system, the instant thermal status of the thermal print head is estimated based upon the history of the dots previously printed. If a particular point on a thermal print head has just completed a task with a high duty cycle, that point will, probably, be hotter that a print head point which has been idle for a period of time. By adjusting the drive energy to the print head points based upon their estimated thermal status, print quality is typically improved and print head overheating is avoided.
One solution to alleviate the print head control problem is to split the processing duties between two microprocessors, both within the printer itself. One logical distribution of functions is to use a first microprocessor for communications management and a second microprocessor for printing management. The second or auxiliary processor is then free to devote its attention to the printing process itself.
U.S. Pat. No. 4,452,136 for PRINTER SUBSYSTEM WITH DUAL COOPERATING MICROPROCESSORS, issued Jun. 5, 1984 to William W. Boynton, et al., teaches the use of one internal microprocessor to manage data communications with a host and a second, cooperating microprocessor to manage the printing and paper handling functions in a high-speed, wire matrix printer. The effect of self-generated heat on a wire matrix print head is generally much less pronounced than in a thermal print head. Consequently, BOYNTON, et al. direct the activities of their auxiliary processor to managing print head position and moving paper, not to compensating for thermal effects in a thermal print head. BOYNTON, et al. incorporate no teaching of a dot history or similar adjustment of the print data; nor is the firing energy adjusted to the wires of the wire matrix print head.
U.S. Pat. No. 5,559,547 for THERMAL PRINTER, issued to Gamal Hagar teaches a system for improving the utilization of a microprocessor. HAGAR discloses an arrangement of buffer storage to improve the printing efficiency of a thermal printer. However, there is no teaching of an auxiliary microprocessor or of a dot history or similar print quality control.
U.S. Pat. No. 6,008,831 for APPARATUS FOR CONTROLLING DRIVING OF THERMAL PRINTHEAD, issued to Masatoshi Nakanishi, et al. teach a rudimentary dot history arrangement for driving a thermal print head. Nakanishi et al. provide a plurality of shift registers to store data corresponding to successive rows of print data. Driving (printing) energy is varied to each point of the thermal print head dependent upon whether the previous data was a xe2x80x9c1xe2x80x9d or a xe2x80x9c0xe2x80x9d (i.e., whether the point was just fired or was idle). There is no teaching of an auxiliary microprocessor or of the application of a dot history print energy control system to a color thermal printer.
It is, therefore, an object of the invention to provide an auxiliary control device to manage print head and paper movement functions in a thermal printer.
It is an additional object of the invention to provide an auxiliary control device in a thermal printer to provide a high-speed dot history control system for single-color printing.
It is another object of the invention to provide an auxiliary control device in a thermal printer to provide a dot history control system for color printing.
It is a further object of the invention to provide an auxiliary control device in a thermal printer compatible with dot print heads and operable with any number of loading inputs.
It is yet another object of the invention to provide an auxiliary control device in a thermal printer which provides at least two previous levels of dot history for single-color printing.
It is a still further object of the invention to provide an auxiliary control device in a thermal printer to provide at least one previous level of adjacent left and right dot history for single-color printing.
It is yet another object of the invention to provide an auxiliary control device in a thermal printer which provides at least one previous level of dot history for color printing.
It is an additional object of the invention to provide an auxiliary control device in a thermal printer which provides at least one previous level of energy level setting for two-color printing.
It is a further object of the invention to provide an auxiliary control device in a thermal printer for up to eight thermal head reloading cycles.
It is a still further object of the invention to provide an auxiliary control device in a thermal printer which provides both 64-point stepper motor acceleration ramp tables and stepper motor current drive tables.
It is another object of the invention to provide an auxiliary control device in a thermal printer which interfaces with standard, external stepper motors. Interfaces provided are for full, half, and micro stopping.
It is an additional object of the invention to provide an auxiliary control device in a thermal printer which provides programmable end dot compensation.
It is a further object of the invention to provide an auxiliary control device in a thermal printer which provides user programmable, on-chip SRAM.
In accordance with the present invention there is provided an auxiliary control device for use in a thermal printer to manage printing and paper movement functions. This frees a main microprocessor for communications and other duties within the printer. Specifically, the auxiliary control device provides a dot history system, both row-to-row and adjacent dots, for use in either a single or multiple color (i.e., two or more color) thermal printer.